(18)F NaF PET/CT Versus Conventional Bone Scanning in the Assessment of Benign Bone Disease

18F-NaF-PET/CT in patients with primary hyperparathyroidism and brown tumors

INTRODUCTION

Brown tumors (BT) are non-neoplastic bone lesions infrequently occurring in patients with long-standing severe hyperparathyroidism (HPT). BT may be identified and characterized using 18-F-sodium fluoride-positron-emission-tomography/computed tomography (¹⁸F-NaF-PET/CT). We present a retrospective series of eight primary hyperparathyroidism (pHPT) patients with BT imaged with ¹⁸F-NaF-PET/CT.

MATERIALS AND METHODS

Imaging assessment included location, diameter, maximum standardized uptake value (SUV_max), metabolically active lesion volume (PET_vol) of BT, total metabolically active bone volume (TMB_vol) per patient and several computed tomography (CT) features of BT. Where appropriate, we analyzed the association between characteristic features of BT in ¹⁸F-NaF-PET/CT, histopathology, clinical symptomatology and laboratory parameters.

RESULTS

In our cohort of 8 patients (median age, 49 years, range, 26-73), 72 BT were found. The mean PET_vol of BT was 89.48 cm³ ± 122.81 cm³ and the mean SUV_max was 17.5 ± 7.8. The total PET_vol of BT per patient correlated positively with serum calcium (r = 0.810, p = 0.015), and negatively with glomerular filtration rate (GFR) (r = - 0.762, p = 0.028). TMB_vol correlated significantly with serum PTH (r = 0.810, p = 0.015), alkaline phosphatase (r = 0.762, p = 0.028), and duration of postoperative hospitalization (r = 0.826, p = 0.011, 24.3 days ± 19.8 days).

CONCLUSION

¹⁸F-NaF-PET/CT is a valuable non-invasive whole-body imaging technique for the assessment of patients with pHPT and BT. TMB_vol is associated with PTH and alkaline phosphatase, and the requirement for intense postoperative calcium substitution, which determines the duration of hospitalization.

Osteoid osteoma: multimodality imaging with focus on hybrid imaging

Osteoid osteoma is a painful, benign, osteoblastic lesion that occurs in younger patients and affects the extremities or the axial skeleton. While plain film findings may suggest the diagnosis, in complex anatomical regions such as the spine, pelvis, wrist and foot advanced imaging modalities are often required. A typical nidus surrounded by sclerosis or cortical thickening characterizes osteoid osteoma on plain radiography and CT. MR is the cross-sectional imaging modality of choice for most musculoskeletal disorders. Unfortunately, extensive accompanying bone marrow oedema, soft-tissue alterations, difficulty detecting the nidus, and lesion locations close to a joint (with reactive arthritis) may make a confident diagnosis of osteoid osteoma by MR imaging difficult. Hybrid imaging with bone-seeking tracers such as SPECT/CT with ^99mTc-labelled bisphosphonates or PET/CT with ¹⁸F-labelled sodium fluoride (¹⁸F-NaF) combines high radionuclide uptake with morphological details and provides accurate diagnosis of osteoid osteoma and additional information for treatment planning. FDG is not the recommended PET tracer because osteoid osteoma is normally FDG-negative, although some osteoid osteomas may show increased FDG uptake. Osteoblastoma, Brodie's abscess and stress fractures may mimic osteoid osteoma on imaging and clinical presentation. Once identified as the pain generator, destruction of the osteoid osteoma nidus by ablation or resection techniques usually leads to complete healing. Image-guided drill excision and radiofrequency ablation are widely used interventions. We review the presentation of osteoid osteoma across all imaging modalities, with special focus on hybrid imaging techniques.